At present the functional improvements gained from surgical reconstruction are estimated from the changes in physical impairment which can be demonstrated by clinical examination. Yet significant discrepancy between demonstrable physical changes and function is a common finding. Rancho Los Amigos Hospital Kinesiology Service has developed a contact-closing footswitch system with measured walkway and timed recording for measuring gait which can be used in a standard clinical setting as well as a sophisticated laboratory. Experience to date demonstrates that velocity and single stance time are the basic parameters that measure a person's general mobility and his weight bearing tolerance on the involved extremity. The objectives of this study are to demonstrate the clinical pertinence of this system by relating it to the physical changes in patients following total hip replacement. The second objective is to demonstrate relationships between function and different types of physical impairment that are customarily identified by either clinical examination or x-ray. The significance is to provide the orthopedic community with a clinically convenient, objective means of measuring gait in order to assess the functional gains from lower extremity surgery. This will permit accurate comparisons of different patients and results among surgical centers.